Precursor for preparing an optical material, method and optical components obtained with same and uses thereof

ABSTRACT

A precursor for the preparation of a material with optical properties modifiable under the action of at least one external parameter, comprising a component A constituted by polymerizable monomers or oligomers, a component B comprising one or several liquid crystals with low molecular weights or polymers and having a type of molecular order that is nematic, cholesteric or smectic or having polymorphism, and 
     at least one surface agent C whose molecules have an affinity both for component A and for component B, and comprising simultaneously one or several chemical groups that can attach chemically to the constituents of component A, and one or several chemical groups comprising a mesogenic portion compatible with the mesomorphic phase of component B, so as to control the interfacial properties between components A, and B during polymerization.

The present invention relates to a precursor for the preparation ofmaterials with optical properties modifiable under the action of atleast one external parameter.

It moreover relates to a process for the production of a component withoptical properties modifiable under the action of at least one externalcontrol parameter.

It further relates to optical components and uses of optical components.

It will particularly find use in the fields of eyeglasses, clocks,windows, visualization, lighting, optical instrumentation, electronicdisplay, which use optical components having very diversefunctionalities such as for example and without limitation:

-   -   transmission with filtering as to wavelength of light, or a        reflection of the latter or a controlled attenuation of light        flow as is the case in the field of windows,    -   various lens effects in the fields of eyeglasses or clocks,    -   a diffusion of light or birefringence involved in certain films        used or in electronic display.

Liquid crystals are commonly used for the construction of displayscreens. Formerly, non-polymer materials were used.

However, for several years, polymers have made their entry into theoptical applications.

There are known at present components which sometimes have spatialmodulation of the index of refraction—in eyeglasses for example—but theyare thus passive, which is to say that locally, the index—or the indicesif the medium is anisotropic: in this latter case there will bedesignated in what follows, by index of refraction, the mean index ofrefraction which takes into account the ordinary and extraordinaryindices of the medium as well as the orientation of the optical axisrelative to the direction of propagation of the light—is fixed once forall time.

For certain other components, it is possible to modify temporally theindex of refraction of the medium as is for example the case in anelectronic display with liquid crystals.

They have however major drawbacks.

Thus, they permit, by applying an electric voltage on the transparentelectrodes disposed on the material, only one uniform modification ofthe light transmitted or reflected by the optical component such as apixel or a segment of the display.

Their possibilities and their fields of application thus are greatlyreduced.

There exists no material or associated process permitting obtaining anactive optical component in which the spatial modulation of the index ofrefraction is predetermined. The process of the present inventionovercomes this thanks to a precursor containing a crosslinkable surfaceagent which permits fixing, at least temporarily, the interfacialproperties between the components which constitute it. By spatialmodulation is meant a modification having any form periodic or not,continuous or not, having or not a gradient form.

At present, when the optical components are transparent without appliedvoltage, it is not possible to obtain a predetermined spatial modulationduring application of a voltage. The present invention permitsovercoming the drawbacks that are encountered at present.

When the components reflect light they do it over a narrow range ofwavelengths which is not adjustable. The present invention permitsovercoming the drawbacks encountered at present.

Certain patents, using or not a surfactant, seek to obtain a spatialmodulation of the optical properties but this modulation is notpredetermined. This is particularly the case in U.S. Pat. No. 4,438,568.The present invention improves this by using a surface agent permittingcontrolling the interfacial properties and simultaneously fixing them,at least temporarily, by reticulation.

Generally speaking, this material can be used in the fields mentionedabove by giving supplemental functionalities which impart value to thepresent application and permit envisaging others. More generally, itserves in all the applications in which an optical component—no matterwhat the nature of its operation: by transmission, reflection,absorption of diffusion of light—is desirable or necessary. In one ofits modifications, the material is passive and its process ofpreparation constitutes an original manner of producing passivematerials with modulation or gradient of index. In another modification,if the modulation of the index of refraction is small, it produces anactive optical component adapted to modify uniformly the lighttransmitted or reflected. By optical component is meant a componentoperating in the field of wavelengths of visible light but also beyondthis range and in particular in the ultraviolet, infrared.

The invention offers both a spatial modulation of the index ofrefraction and a control for the modification of the optical propertiesof the component.

Other objects and advantages will become apparent from the descriptionwhich follows.

The present invention relates to a precursor for the preparation of amaterial with optical properties modifiable under the action of at leastone external parameter. This precursor which comprises:

-   -   a component A constituted of monomers or polymerizable        oligomers,    -   a component B comprising one or several liquid crystals with        small molecular weights or polymers and having a type of        nematic, cholesteric or smectic molecular order or having        polymorphism,        is characterized in that it comprises moreover:    -   at least one surface agent C whose molecules have an affinity        both for component A and for component B and comprising        simultaneously one or several chemical groups that can attach        chemically to the constituents of component A, and on the other        hand, one or several chemical groups comprising a mesogenic        portion compartible with the mesomorphic phase of component B,        so as to control the interfacial properties between said        components A, B during polymerization,        for the preparation of a material having a spatial modulation of        its optical properties.

This precursor could be present in the embodiments cited hereafter:

-   -   the surface agent C is polymerizable.    -   The surface agent C comprises component A.

Component B comprises at least one liquid crystal with dielectricanisotropy changing sign under external action or parameters.

Component B comprises at least one liquid crystal with positivedielectric anisotropy.

Component B comprises at least one liquid crystal with negativedielectric anisotropy.

It comprises a photo-initiator compound for the polymerization byphotochemical action.

Component B comprises one or several additives selected from colorants,photochromic compounds and chiral dopants, mesomorphic or not.

It has the weight proportions:

-   -   60 to 80% component A    -   40 to 20% component B    -   the surface agent C is 1 to 5% of the whole of components A and        B, by weight.

It has, by weight proportion:

-   -   70 to 97% of component B    -   30 to 3% of surface agent C.

The present invention also relates to a process for the production of acomponent with optical properties modifiable under the action of atleast one external control parameter, characterized by the fact

that the precursor according to the invention is used,

that said precursor is subjected to the action of spatial modificationmeans of its index of refraction,

that there is fixed, at least temporarily, the spatial modulation of theindex of refraction by polymerization.

This process could have the following modifications:

the polymerization and the action of spatial modulating means aresimultaneous.

The spatial modulation means are selected from means for the applicationof an electric field, heating means, a variable concentration of one ofthe chemical species or of the means for application of luminousintensity.

A mold or a substrate is used for deposition of the precursor,

electrically conductive electrodes of the desired shape are positionedin the mold or on the substrate to constitute one of the spatialmodulation means of the index of refraction by means of the use of anelectrical field,

the precursor is positioned in the mold or on the substrate.

The electrodes are of transparent materials such as indium tin oxidesdeposited on transparent materials such as glass or a plastic materialor else conductive polymers to produce a photo-induced polymerization.

Electrodes are used as the external control parameter.

The invention also relates to an optically active component of the typeof lenses and diffraction gratings that can be obtained by the processcharacterized by the fact that it comprises an active film produced fromthe precursor and two transparent covering electrodes, each covering onesurface of the active film or deposited on a substrate and whoseinternal surface in contact with the active film is electricallyconductive to apply an electric field between the two internal surfaces,as well as an active component that can be obtained by the process,characterized by the fact that it comprises at least one plate or activefilm made from the precursor and forming or incorporating itself in aconstruction wall.

This latter component could be such that

the plate or active film is selected to be transparent without theaction of the external control parameter.

the plate or the active film is selected to be reflective over a rangeof wavelengths whose width is adjustable by the spatial modulationmeans.

The invention finally relates to the application of a component withmodifiable optical properties under the action of at least one externalcontrol parameter adapted to be obtained by the process with theformation of an infrared modulator.

It also concerns the application of a component with modifiable opticalproperties under the action of at least one external control parameter,adapted to be obtained by the process with the formation of an activecomponent reflecting light.

The accompanying drawings are given by way of indicative examples andare not limiting. They represent a preferred embodiment according to theinvention. They permit easy comprehension of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show an example of application of the invention to aglazed wall.

FIGS. 3 to 5 show variations of the quantity of transmission of anoptical component as a function of the applied control voltage,according to three examples.

FIG. 6 shows the case of an active component reflecting light over awide spectral band and attained by spatial modulation in the thicknessof the component.

FIGS. 7 and 8 shows variations of reflectivity of a component as afunction of the wavelength, according to two other examples.

FIGS. 9 to 11 show the results obtained for two cases of application ofthe invention to an active optical component of the infrared modulatortype.

In what follows of the description, there is meant by action of anexternal parameter the use of an external energy source andparticularly: an electrical field (difference of applied potential), alight flux of natural or artificial origin.

Moreover, the expression active optical component corresponds to acomponent whose optical properties are modifiable under the action of anexternal parameter.

The precursor of the material uses mixtures comprising:

-   -   A component A constituted by monomers or oligomers, chiral or        not, which by polymerization in the presence of other compounds        will provide a homogeneous or heterogeneous plastic material        such as a gel or a micro-composite. Numerous compounds and in        particular those adapted to lead to photo-induced polymerization        reactions, are suitable. There is for example found in the work        of J. Fouassier: Photoinitiation, photopolymerization and        photocuring (Hanser, Munich, 1995, page 145) a description of        several typical reactions in cases such as those of mono and        multifunctional acrylates, unsaturated polyester resins, or else        thiol-ene resins. Various commercially available mixtures using        such monomers and oligomers are sold by companies such as        Norland® or Protex®.    -   A component B comprised by liquid crystals or mixtures of liquid        crystals of low molecular weight or polymers and having a type        of molecular order conventionally provided by these compounds,        which is to say nematic, cholesteric or smectic or having        polymorphism. These liquid crystals have either a negative or a        positive optical anisotropy or else a dielectric anisotropy        changing in sign with a parameter such as the frequency of an        applied electrical field or temperature. They can be doped with        different additives such as colorants, photochromic compounds,        chiral dopants that are mesomorphic or not.

The nematic, cholesteric, or smectic mixtures can be formulated frompure components commercially available or purchased once formulated byspecialized producers such as Merck®, Chisso®, Dainippon Ink®, ValiantFine Chemicals®, Rolic®. The compounds used in the examples can bereplaced by mixtures using commercial products such as mixtures E7 orE90 of Merck® which are nematic with strong dielectric anisotropy, thechiral dopants of the series CE or CB15 or else C15 or S1082 or S811 areobtained also from Merck®. Finally, liquid crystal mixtures having achange of dielectric anisotropy as a function of the frequency, can bereplaced by mixtures 2F-3333, 2F-3361 from Rolic®.

A component C constituted by a surface agent, chiral or not, most oftenpolymerizable or a mixture of surface agents permitting, duringpolymerization of the precursor, to control the interfacial propertiesbetween the liquid crystal and the polymer and to induce a temporaryspatial non-uniformity of the material. By temporary is meant anon-uniformity which can be modified or even cancelled by the action ofan external parameter such as an electrical field. The surface agent isselected such that the molecules which comprise it have a doubleaffinity: on the one hand for the liquid crystal and on the other handfor the polymer. This affinity is manifested for example by theformation before polymerization of a single phase by mixture with thecomponents A and B. These are particularly molecules comprisingsimultaneously a group that can attach chemically to the monomers oftype A and on the other hand to a chemical group compatible with themesomorphic phase of type B, in particular this group can itself bemesogenic. Numerous compounds such as those of the company Wacker-ChemieGmbH® such as photopolymers CC3939 or CC4070 or else such as theproducts RM9 or CM14 or CM7 of Polymage or else in certain cases RM257of Merck®, are suitable for component C. The compounds LC 242/756 of thePaliocolor® series of Bayer® can also be used. If for example thecompound of type A contains, in addition to the photoinitiator, monomersof the acrylate or methacrylate type, there can be used a component Cconstituted by comb polymers having acrylate or methacrylate reactivegroups and containing moreover mesogenes selected to be compatible withthe component B. Photopolymerizable liquid crystal silicones such asCC3939 or CC4039 or else CC4070 of Wacker-Chemie GmbH® which aremixtures of reactive monomers and comb polymers with a siloxane skeletonand a methacrylate function in the side chain, satisfy these criteriaquite well, because the side groups comprise moreover chiral mesogenesderived from cholesterol and non-chiral, which are both compatible withthe liquid crystal phase, and are in a ratio which determines thechirality of the mixtures.

Most often, the two principal components A and B, which is to say themonomers and the liquid crystals, form the principal portion of thematerial, and the surface agent C is present in only a small fraction(less than several percent), however an important variant of thematerial includes the case in which A does not exist but in which themolecules of surface agent C comprise polymerizable groups such as A.

The relative proportions of A and B are anywhere within the range 0 to100%, however in practice two cases are particularly important:

-   -   The one in which A is predominant: typical formulations being        for example: A comprised between 60 and 80%, B comprised between        40 and 20%, and surface agent C being selected as a small        percentage of the assemble A+B (for example 3%). For a mixture        comprising 70% A, 30% B and in which surface agent C represents        3% of the whole, the relative compositions of A, B, surface        agent C will be indicated by 70/30//3.    -   The one in which B is predominant: typical formulations being        for example B comprised between 70 and 97% and surface agent C        comprising groups of type A, comprised between 30 and 3%.

Moreover, when the compounds A and B are polymerized by photochemicalaction, there is systematically added to them a photoinitiator in asmall proportion which represents in general 1 to 3% of their weight.The photoinitiators used come from Ciba-Geigy® and are sold under themark Irgacure®. Most often, Irgacure® 907 in a proportion of 2% ispreferred.

From the precursor set forth herein, it is possible to obtain a materialpermitting producing an active optical component.

A process for this purpose also forms a part of the invention. There arehereafter described the principal phases in a preferred embodiment.

-   -   There is induced before or in the course of polymerization by        means such as an electric field, a spatial modulation of        temperature, or of concentration of one of the chemical species,        or else by luminous intensity, a temporary spatial        non-uniformity of the material and there is utilized        polymerization at a point or in a region more extended to        conserve this non-uniformity or the non-uniformity which results        from it. The modulations in question relate to the quantities        such as temperature, concentration or concentrations of certain        chemical species, or else the illumination can have or not the        form of gradients.

A homogeneous material, which is to say having a single phase, can bespatially non-uniform; the causes of non-uniformity can be various andin particular associated with a different orientation of the moleculeswhich modulate locally the index of refraction.

A heterogeneous material comprising two or several phases can moreoverbe spatially non-uniform; in this case, the spatial non-uniformitydepends on the phases present: thus for example, in the case of amicro-composite having micro-inclusions, the parameters such as thedensity or size of the micro-inclusions are modulated spatially, whilstfor a gel, it is the parameters such as density or shape or orientationof the polymeric network which are spatially modulated.

The spatial non-uniformity can be of any type: in a film for example itis axial, which is to say perpendicular to the plane of the film, orradial such as that relative to a radial gradient from a point on thesurface of the film or else of any shape that is periodic or not. Itpermits inducing a spatial modulation of the index of refraction of thematerial. The examples cited later permit exactly describing thisproperty.

The spatial non-uniformity of the material is created by processes suchas a spatially modulated electric field, a temperature gradient. Thenon-uniformity is also generated by polymerization as in the case of aphotopolymerization in which the UV radiation penetrates more or lessdeeply into the thickness of the specimen or else when the differentportions of the specimen are not subjected to uniform UV radiation suchas that which can be produced thanks to a set of masks or any otheroptical means.

The polymerization can be carried out at a point—or in a so-called locallimited zone—or in a more extended zone. For example, the index ofrefraction or the mean index of refraction can be locally modified ifthe medium is anisotropic, by an electric field or the local zone ispolymerized where the index of refraction has a desired value.

The inhomogeneity is more or less important. The limit case is that oflow inhomogeneity leading to a homogenous material. When thepolymerization produces a phase separation leading to a microcomposite,the inhomogeneity of the optical properties can result from a spatialinhomogeneity of morphology of the composite.

The process of the invention and the precursor also presented, permitobtaining optical components adapted to find their application innumerous fields.

There is described hereafter a possibility for obtaining such opticalcomponents.

-   -   Optical components are obtained by the shaping of the material,        or of materials associating said material with other materials.        This shaping is carried out on the precursor, by means such as        deposit on substrates or filling of a mold, a reservoir or a        cell on the walls of which have been deposited transparent        electrodes of various shapes. The transparent electrodes of        various shape can also be deposited on the polymerized material        used in that condition or surfaced.

The shaping of said material, or of the constituent materials, forobtaining an optical component, takes place by conventional means whichdepend on the shape of the component.

If it is a film, different processes of manual or automatic spreadingsuch as screeds or “coaters” or rollers or else serigraphy can be used.It is also possible to place the precursor in an elongated cavity ofregular and flat shape to be polymerized there and to form a film, orelse it can be placed in a cavity of any shape before polymerization. Inthe case in which the inhomogeneity is obtained by an electrical field,electrodes in the selected shapes are disposed on the internal walls ofthe cavity. When the polymerization is optically assisted, theseelectrodes are transparent and made from materials such as indium tinoxides (ITO) which can be engraved to have predetermined shapes, or byany other process permitting obtaining transparent and conductiveelectrodes, such as those which use solutions of conductive polymers. Ifit is a film, it can be interesting to apply an electric field over allor a portion of the latter thanks to plastic supports that do not havegood adherence with the polymerized film. It is thus possible toseparate the supports of the active film after polymerization withoutaltering it. Thus other transparent electrodes (CPP 105 T of Bayer® forexample) permitting acting on the properties of the film, can bedeposited eventually on the latter. The electrodes permitting formingthe film and those permitting controlling it, can have either the sameshape or a different shape. Before depositing the electrodes, thematerial can be surfaced to give it the desired shape.

-   -   The control of the component is effected by transparent        electrodes such as ITO deposited on transparent glass or plastic        substrates placed on the active film, or solutions of conductive        polymers deposited directly on the constituent or constituents        of the optical component. The control electrodes can be        different from the electrodes which if desired serve to create        the spatial inhomogeneity, which permits modifying in a way that        is most often reversible, the temporary spatial non-uniformity        of the material and hence its optical properties.

When the transparent electrodes are constituted by conductive polymers,the processes such as serigraphy are used for deposition. Otherconductive materials having good transparency such as glass or plasticsubstrates covered with ITO are commercially available from thecompanies IST, Balzers, Southwall. They can also be made inlaboratories, in particular on glass by methods such as those describedby T. Kanbara, N. Nagasaka, T. Yamamoto in Chem. Mater. 1990, 2, 643 to645. In the case of optical components formed by associating severalelectrically controllable materials, the association of these latter cantake place in different ways in particular by superposition. Stacking,not necessarily flat, is carried out by superposing either materialscomprised between two substrates or materials without a substrate onwhich are deposited transparent electrodes. The different stackedmaterials can be controlled independently with voltages and frequenciesof independent control signals.

As indicated above, the invention has the advantage of widening thefield of application of active optical components.

By way of example illustrating this, there are given hereafter severalmodifications of the invention according to the desired use. Indicativecompositions of precursor are also given in each case. Similarly, a modeof effecting the spatial modulation and the control, is mentioned.

I—Active Optical Component of the Lens Type and Diffraction Grating

Composition: A mixture comprising a thiol-ene resin of the type NOA65(Norland®) and a nematic liquid crystal with positive anisotropy of theYM6 type (Valiant Fine Chemicals®) whose ordinary index is very near theindex of the thiol resin, and a polymerizable surface agent of the typeRM9 (Polymage) is placed between two thick plastic films of 50micrometers (microns) and covered with ITO (IST). The ITO surfaces arein contact with the mixture and the spacing between the two plasticfilms is 30 microns. The mixture also contains a photoinitiator(Irgacure® 907 of Ciba-Geigy®) whose weight proportion of RM9 is 2%. Therespective resin/crystal liquid/additive proportions are respectively70/30/3.

Induction of non-uniformity: A mask constituted alternately of blackportions and transparent portions is placed on the upper sheet. Thedesigns of the mask represent a series of concentric circles forming aSoret grid. It is a diffraction grid with symmetry of revolution havinga radial periodicity according to the square of the radius. There isapplied a strong field (2 V/micron) to the film and there is carried outa polymerization under the field with for irradiation parameters: 0.6mW/cm² for 10 minutes. Only the portions that are not covered by theblack regions of the mask are irradiated. Given the positive dielectricanisotropy of the liquid crystal, the field orients the moleculesperpendicularly to the plastic films, and thanks to the surface agent,this orientation is maintained after the field is turned off. Without asurface agent, this orientation is not maintained. The component is thenirradiated without a dielectric field and after having removed the mask.The previously irradiated zones remain identical, which is to saytransparent, whilst the other zones become opaque white.

Shaping: The resulting sandwich comprised by two plastic films coveredwith ITO (constituting the control electrodes) within which has beenformed the active film, constitutes in this condition the opticalcomponent.

Control for the modification of optical properties: The optical elementobtained, illuminated with monochromatic light and with no appliedfield, functions as a Soret grating. The application of the electricfield cancels this function. A field of IV/micron applied between thetwo ITO films renders the component completely transparent. The sameprinciple is applicable to any type of component using the defractiveoptics of a micro-grating or Fresnel lens.

The YM6 can be replaced by mixtures of positive dielectric anisotropysuch as mixtures of E7 or E90 of Merck®. The thiol-ene resin NOA65 canbe replaced by Norland® resins such as NOA68 or NOA81 or other types ofresins such as acrylates such as HM20 (Aldrich®) or else a mixture ofthese resins. Thus, the mixtures NOA65/HM20 in different proportionshave been used with success.

The RM9 can be replaced with components such as CC3939 or CC4070 ofWacker-Chemie GmbH®.

II. Active Optical Component having High Transparency at Rest andAdapted to be Integrated into a Wall of a Building in the Form of aWindow of the Venetian Type

There are presented in this portion several versions of an opticalcomponent obtained from precursor mixtures with which is associated foreach of the mixtures a specific process of preparation. All theseprecursors lead to carrying materials of the same functionality, that ofan active optical component having high transparency without applicationof an electric field, and used as an optical component in a window ofthe Venetian type.

FIGS. 1 and 2 show this arrangement.

II-1 EXAMPLE II-A

Composition: A mixture comprising on the one hand a thiol-ene resin ofthe NOA65 type (Norland®) and an HM20 resin (Aldrich®) in respectiveweight proportions of 80/20 and a liquid crystal of the KDK07 type(Polymage) whose frequency of cutting, which is to say the frequency forwhich the dielectric anisotropy changes in sign, is 1 KHz, and apolymerizable surface agent of the type RM9 (Polymage) to which is addeda photoinitiator which represents 2% by weight of the RM9 compound, isdisposed between two plastic films (3) (20×30 cm) of 125 micronsthickness, having a resistivity of 70 ohms per square, covered with ITOfrom the IST company. The ITO surfaces are in contact with the mixtureand the spacing between the two plastic films is 50 microns. Therespective proportions of resin/crystal liquid/additive are respectively70/30//3. The mixture also contains a photoinitiator (Irgacure® 907 ofCiba-Geigy®) whose weight proportion of the RM9 is 2%. The plastic filmshave first been assembled by pressing after deposition of a peripheralcement joint deposited by serigraphy, the resulting cell has twoopenings to carry out filling by capillarity, the thickness of the spacebetween the two plates is calibrated by adding to the cement balls of acalibrated diameter and calibrated spacers between the plastic films.The latter can be obtained from from Dyno® particles AS, Lillestrome,Norway or Duke Scientific Corporation®—Palo Alto, USA.

Induction of non-uniformity: A mask comprising successive stripes ofunequal width—in our example respectively 1 mm and 20 mm—and alternatelytransparent lines (1 mm) and black lines (20 mm) is provided, called apositive mask. A negative mask is also provided with black stripes of 1mm and transparent stripes of 20 mm.

The so-called negative mask is placed on the upper plastic film andthere is carried out a polymerization under a field whose value isrelatively high (2V/μm) and of low frequency (500 Hz). Low frequencymeans a frequency substantially lower than the cutoff frequency of theliquid crystal. The polymerization carried out under wide bands resultsin transparent zones and the orientation of the moleculesperpendicularly to the plane of the film is maintained after cutting offthe electric field, thanks to the surface agent RM9. It is notmaintained if this agent is not present.

The so-called positive mask is superposed on the plastic film at theplace previously occupied by the negative mask, and so the zonespreviously exposed are hidden and the zones previously hidden are nowexposed. There is thus carried out a polymerization under a field, whosevalue is relatively high 2 V/μm, of high frequency (20 KHz), highfrequency meaning a frequency substantially greater than the cutofffrequency of the liquid crystal. The polymerization which takes placeunder the narrow strips results in transparent zones and the orientationof the molecules parallel to the plane is maintained after cutting offthe electrical field thanks to the surface agent RM9.

Shaping: The resulting sandwich comprised by the two plastic filmscovered with ITO within which has been formed the active film (2) isintegrated into a glazed element constituting a window. It is placedwithin a double pane on the external surface. The double pane (4, 5), ifdesired provided with an anti-UV film on its external surface, is shownin FIG. 1. The designs in the form of wide rays (10) occupy all or aportion of the window and are replaceable by designs of any form. By wayof example there is shown an assembly of rectangular designs (11).

Control: A control device (7) connected to detectors (6) permitsautomatically controlling the optical properties of the wide rays of theactive film and hence the flow of light which passes through the window.The application of a high frequency field (20 KHz) leaves the narrowrays transparent but induces opacity in the wide rays (10) which becomeall the more opaque as the field is elevated as indicated in FIG. 3,which shows the transmission of the window as a function of the appliedvoltage.

The thio-ene resin NOA65 can be replaced by Norland resins such as NOA68or other resins such as acrylates, the liquid crystal KDKO7 can bereplaced with liquid crystals such as 2F-3333 and 2F-3361 of ROLIC®.

II-1 EXAMPLE II-B

Composition: The mixture of a photo-crosslinkable monomer (PN393 ofMerck®), of a liquid crystal (KDK07) with dielectric anisotropy changingin sign with frequency, and a polymerizable surface agent (RM9) isplaced between two glass plates covered with ITO on one of its surfaces.The ITO surfaces are in contact with the mixture and the spacing betweenthe two glass plates is 8.5 microns. The relative concentrations are30/70/3. The mixture also contains a photoinitiator (Irgacure® 907 ofCiba-Geigy®) whose weight proportion relative to RM9 is 2%. The glassplates are first assembled by pressing after depositing a peripheralcement joint by serigraphy, the resulting cell has two openings to carryout filling by capillarity, the thickness of the space between the twoplates is calibrated by the addition of balls of calibrated diameter tothe cement.

Induction of non-uniformity: By using the positive mask of example II-A,the narrow rays (1 mm) are irradiated with a power of 0.6 mW/cm² for 10minutes and in the presence of a high frequency electric field (100 V onthe specimen, frequency of 20 KHz) applied to the active film by meansof two layers of ITO. There is then carried out a cross linking of thefilm with the negative mask of example II-A and the application of a lowfrequency field (100 V on the specimen, frequency 500 Hz). Theorientation of the molecules of the liquid crystal in the wide zones isperpendicular to the surface and the zone in question appearstransparent. The film remains transparent after cutting off the field,thanks to the surface agent.

Shaping: The resulting sandwich comprised by the two glass platescovered with ITO within which has been formed the active film, is placedin a glass component as in example II-A.

Control: The application of a high frequency field (10 KHz) induces anopacification of the wide rays which becomes the more opaque as thefield rises. The transmission of the wide rays as a function of theapplied voltage is shown in FIG. 4, in which the responses at 1 and 10KHz have been shown. The control which permits passing from transparencyto opacity, is carried out at 10 KHz by increasing the voltage. Anothercontrol mechanism consists in modifying the frequency of the fieldapplied between 1 and 10 KHz while leaving the window under a voltage of110 V.

The KDK07 can be replaced with the mixture 2F-3361 of ROLIC®. The RM9can be replaced by components such as CC3939 or CC4070 of Wacker-ChemieGmbH®.

II-1 EXAMPLE II-C

Composition: The mixture of a chiral liquid crystal (KDK07) withdielectric anisotropy changing in sign with the frequency, containing achiral dopant NXO (Polymage) and a polymerizable surface agent (RM9) isplaced between two glass plates covered with ITO on one of the surfaces.The ITO surfaces are in contact with the mixture and the spacing betweenthe two glass plates is 15 microns. The relative concentrationsKDK07/NXO are 91/9 and the RM9 represents 7% of the whole. The mixturealso contains a photoinitiator (Irgacure® 907) whose weight proportionon RM9 is 2%. The glass plates have first been assembled by pressingafter the deposition by serigraphy of a peripheral cement joint. Theresulting cell has two openings to carry out filling by capillarity, thethickness of the spacing between the two plates is calibrated by addingballs of calibrated diameter to the cement.

Induction of non-uniformity: By using the positive mask of example II-A,the narrow rays (1 mm) are irradiated with a power of 0.6 mW/cm² for 20minutes and in the presence of a low frequency electric field (3 V permicron, 1 KHz) applied to the active film by means of the two ITOlayers. The orientation of the molecules of the liquid crystal in thiszone is perpendicular to the surface and the zone in question appearstransparent. There is then carried out a cross linking of the film withthe negative mask of example II-A and the application of a highfrequency electric field (3 V per micron, 20 KHz). The active film istransparent after cutting off the field.

Shaping: The resulting sandwich comprised by two glass plates coveredwith ITO within which has been formed the active film, is placed in aglazed component of the double glazed type as in example II-A.

Control: The ultimate application of a low frequency (50 Hz) fieldmodifies the transparency of the wide rays to render them the moreopaque as the amplitude of the applied field rises, as indicated in FIG.5. NXO can be replaced by S811 of Merck®.

RM9 can be replaced by components such as CC3939 or CC4070 ofWacker-Chemie GmbH® or CM7 and CM14 of Polymage.

The KDK07 can be replaced by mixtures 2F-3333 and 2F-3361 of ROLIC®.

III—Active Optical Component Operating Over a Wide Spectral RangeObtained by Spatial Modulation in the Thickness of the Component andAssociation of said Active Component with Other Active Components toExtends its Range of Utilization.

EXAMPLE III-A

Active optical component reflecting light over a wide spectral band andobtained by a spatial modulation throughout the thickness of thecomponent, adapted to be integrated into a window.

Composition: A liquid crystal mixture, constituted by a nematic withhigh positive dielectric anisotropy (BN5 Polymage) and a right chiralliquid crystal (NXL, Polymage) such that the selective reflectionobtained for the mixture will be in the ultraviolet (UV), the visible orthe infrared, is used. Thus a mixture containing respectively 64 partsof BN5 and 36 parts of NXL produces a selective reflection of 400 nm.The addition of a chiral surface agent (RM9) in a small proportion (lessthan 20%) that can polymerize under UV and whose interval has an inversechirality (left) from the liquid crystal mixture permits modifyinggreatly the selective reflection because the direction of rotation ofthe two mixed chiral compounds are reversed. Thus the selectivereflection passes from 400 nm without RM9 to 440 nm with 3% of surfaceagent, 490 nm with 6%, 540 nm with 10%.

Introduction of non-uniformity: The mixture with 10% is placed betweentwo glass plates covered with ITO on one of its surfaces such that theITO surfaces will be in contact with the liquid crystal. The mixture isirradiated with UV from above such that there exists a decrease of UVpower when placed at a greater and greater depth into the interior ofthe resulting film. This effect is obtained either by including in themixture, at a very low proportion (less than 1%), a UV absorbent of theTinuvin® type produced by Ciba-Geigy®, or by using a very lowirradiation power (0.06 mW/cm²) such that when the polymerizable RM9 isconsumed in the exposed zones, a movement of the molecules of thiscompound takes place from the weakly exposed zones in which itsconcentration is great, toward the more strongly exposed zones where theconsumption of the compound gives rise to impoverishment of the monomernot yet polymerized. The decrease in the penetration of the irradiationgives rise to an increase of an inhomogenous microcomposite structureconstituted of polymer and liquid crystal, denser toward the surfacenear the UV (upper surface of the specimen). The greater the density ofthe polymer network, the greater the selective reflection of the chiralmicrocomposite polymer/liquid crystal has a longer wavelength. The upperportion of the optical film formed thus reflects selectively the lightcorresponding to the highest wavelengths and the lower part selectivelyreflecting the light corresponding to the lower wavelengths. By thisprocess of production there has thus been produced a gel polymer whosedensity varies with the thickness of the specimen. This spatialinhomogeneity of density of the gel polymer results in a reflection ofthe light in a wide spectrum and with a metallic gray color of thespecimen. It is to be noted that the dissymmetry of the gel results inthe reflection band not being identical according to whether thespecimen is observed from above (surface for penetration by UV) or frombelow. The thickness of the specimen and the operative conditions havebeen selected such that the specimen will be active, which is to saythat a reversible modification of the orientation of the liquid crystalexists in all the portions of the gel under the influence of an appliedfield whose maximum amplitude is 220 V.

Shaping: The resulting active optical component is, as in example II-A,integrated into a double glazing used as a glazing component for thecontrol of solar flux.

Control:

FIG. 7 compares the spectral bands obtained before and afterirradiation. The width of the initial band of 70 nm is exceeded at 200nm. The same type of result is obtained by replacing the component RM9by a compound such as RM257 of Merck®; the enlargement of the spectralband still exists but is weaker. The same type of enlargement isobtained with a small percentage of Tinuvin® (1%) added to theprecursor. FIG. 8 shows the effect of the application of a voltage of 95V on an optical component, of 15 microns thickness and reticulated witha power of 0.09 mW/cm². Before application of the voltage, the specimenhas a wide reflection band of 200 nm centered about 550 nm. The appliedvoltage permits eliminating this reflection band. The elimination of thevoltage permits returning to a condition very near the originalcondition. FIG. 6 shows the variations of the wavelength of reflectionassociated with the interval of the chiral liquid crystal structure as afunction of the concentration of the functional monomer RM9. To obtaingood reversibility, the concentration of chiral monomer should not betoo great (<10%) so that the gel formed in the upper portion of the filmwill not be too dense thereby to permit response in an electric fieldwhich will not be too slow.

The optical component with a wide band of reflection, electricallycontrollable and integrated into a window, can also be used in otheroptical applications requiring a wide band reflection.

Other nematic mixtures available commercially are for example YM6 ofValiant Fine Chemicals, E7, E90 and the chiral compounds such as CE1 toCE11 or CB15 or else C15 sold by the Merck® company can be used in thistype of application.

RM9 can for example be replaced by components such as CC3939 or CC4070of the Wacker-Chemie GmbH®.

EXAMPLE III-B

Optically active component operating in a very wide range of spectra,obtained by a spatial modification through the thickness of thecomponent and association of said active component with other activecompounds to extend it scope of use.

An active film, comprised between two plastic substrates covered withITO, analogous to that of example II-A, is produced. After preparation,the plastic substrate covered with ITO is withdrawn from the uppersurface of the active film. On this same surface there is then depositeda transparent conductive coating constituted by a solution of conductivepolymer CCP 105 T of Bayer® and a layer of the constituent material ofexample III-A. On the upper portion of this latter layer, a plastic filmcovered with ITO is emplaced and constitutes the second transparentelectrode of the material analogous to that produced with III-A. Theprocess of polymerization used is identical to the one present inexample III-A. An active bilayer component thus obtained in which eachactive layer, which can be controlled independently, has the propertiesdescribed above.

IV—Optically Active Component of the Infrared Modulator Type

EXAMPLE IV-A

Optically active component modulating the light over a wide spectralband in the spectrum of wavelengths near infrared and obtained byspatial modulation through the thickness of the component.

Composition: There is used a nematic (YM6) whose dielectric anisotropyis positive and the chiral compound is constituted by a mixture of AOLand CML (Polymage) and of an active chiral RM9 as previously. Themixture is placed between two glass plates of 1.1 mm thickness coveredwith ITO on which a film of brushed polyimide has first been deposited.They can be preferably replaced by a material such as polypropylenehaving a better transmission in the near infrared and which is coveredwith a transparent electrode. The irradiation takes place at 0.06 mW/cm²for 15 minutes. For a thickness of the mixture of 11 microns and ofrelative proportions YM6/AOL/CML of 80/6/3 to which there is added 3% ofRM9 by weight of the total, the observed reflection wavelength is in thenear infrared (0.9 micron) (FIG. 9).

Introduction of non-uniformity: Procedure as in example III-A.

Shaping: The resulting sandwich comprised of the two glass platescovered with ITO and within which has been formed the active film,constitutes in this condition the optical component.

Control: The application of a low frequency voltage (50 Hz) modifies thereflection band and hence the transmission of the component. Theapplication of a voltage of 95 volts renders the component diffusive anda return to 0 volts permits recovering the initial reflectivity (ortransmission). FIG. 10 shows the effect of voltage on transmission. Avoltage of 180 volts renders the specimen transparent to infrared. TheYM6 can be replaced by the compounds E7 or E90 of Merck® or BN5 ofPolymage.

The RM9 can be replaced by a component such as CC3939 or CC4070 ofWacker-Chemie GmbH®.

The AOL and the CML can be replaced by compounds such as ZLI 3786 ofMerck®.

EXAMPLE IV-B

Optically active component modulating the light over a wide spectralband in the region of wavelengths of visible light and of near infraredand obtained by a spatial modification in the plane of the component.

Composition: There is used a nematic YM6 whose dielectric anisotropy ispositive, the chiral compound NXL and a chiral additive RM9 as inexample IV-A. The mixture is disposed between two glass plates of 1.1 mmthickness covered with ITO, on which a film of brushed polyimide hasfirst been deposited. The irradiation takes place at 0.06 mW/cm² for 15minutes. For a thickness of the mixture of 8.5 microns and the relativeproportions YM6/NXL of 63/27 to which 7% RM9 is added, the wavelength ofobserved reflection is in the near infrared (0.7 microns).

Introduction of non-uniformity: The preceding spatial modulation carriedout (example IV-A) in a direction perpendicular to the glass plates ofthe component, can be completed by a modulation parallel to the latter.One of the means consists in having a mask which has for its design aseries of alternately black and transparent rays or any other designhaving a spatial modification of the levels of gray, and placing itbetween the film and the UV irradiation. The use of a mask comprises aseries of alternately black and transparent zones (in the present casewith a width of 1 mm for both types of bands) shows that the exposedzones reflect a weaker wavelength than the wavelength with liquidcrystal material before irradiation and that the irradiated zones have avery marked enlargement, connected in particular to the diffusion of themonomers from the unexposed zones toward the exposed zones (FIG. 11).FIG. 11 shows the spectral enlargement obtained: the initial strip hastripled in width. Although initially it was in the visible and at theupper limit of this latter, it now encroaches on the near infrared.

Shaping: The resulting sandwich comprised by two glass plates coveredwith ITO, within which has been formed the active film, constitutes inthis condition the optical component.

Control: It is effectuated as in example IV-A

The RM9 can be replaced by components such as CC3939 or CC4070 ofWacker-Chemie GmbH®. The NXL can be replaced by a compound such as ZLI3786 of Merck®.

In example IV-B, the width of the spectral band which it is possible tomodulate is about 250 nm. Wider bands (up to 400 nm and more) can beobtained by modification of the birefringence of the mixtures and of thewavelength of reflection before enlargement. A high birefringence and aninitial high wavelength of reflection lead to an important naturalenlargement. This natural enlargement is increased by spatial modulationto obtain a supplemental induced enlargement. The modulations in theplane of the component and perpendicular to this latter can of course becombined for this purpose.

REFERENCES

-   1. Optical component-   2. Active film-   3. Transparent electrodes-   4. External glass plate-   5. Internal glass plate-   6. Detector-   7. Means for applying an electric field-   8. Layer of air-   9. Wall-   10. Opaque rays-   11. Opaque designs

1. A precursor for the preparation of a material with optical propertiesmodifiable under the action of at least one external parameter, whichcomprises: a component A comprising polymerizable monomers or oligomers,a component B comprising one or several liquid crystals of low molecularweight or polymers and having a type of molecular order that is nematic,cholesteric or smectic or having polymorphism, and at least one surfaceagent C whose molecules have an affinity both for component A andcomponent B and comprising simultaneously one or several chemical groupsthat can attach chemically to the constituents of component A, and onthe other hand, one or several chemical groups comprising a mesogenicportion compatible with the mesomorphic phase of component B so as tocontrol the interfacial properties between said components A, B duringpolymerization.
 2. The precursor according to claim 1, wherein thesurface agent is polymerizable.
 3. The precursor according to claim 1,wherein component B comprises at least one liquid crystal withdielectric anisotropy, changing in sign under the action of the externalparameter or parameters.
 4. The precursor according to claim 1, whereincomponent B comprises at least one liquid crystal with positivedielectric anisotropy.
 5. The. precursor according to claim 1, whereincomponent B comprises at least one liquid crystal with negativedielectric anisotropy.
 6. The precursor according to claim 1, whereinsaid precursor further comprises a photoinitiator compound forpolymerization by a photochemical action.
 7. The precursor according toclaim 1, wherein component B further comprises one or several additivesselected from colorants, photochromic compounds and chiral dopants thatare mesomorphic or not.
 8. The precursor according to claim 1, whereinsaid precursor has in weight proportion: 60 to 80% of component A 40 to20% of component B and wherein said surface agent C represents 1 to 5%of the whole of components A and B, in weight proportions.
 9. Theprecursor according to claim 1, wherein said precursor has, in weightproportions: 70 to 97% of component B 30 to 3% of surface agent C andcomponent A.
 10. The precursor according to claim 1 wherein component Acomprises monomers selected from acrylates or methacrylates, component Bis a liquid crystal or a mixture of liquid crystals, and wherein thesurface agent C comprises comb polymers having reactive groups selectedfrom acrylates or methacrylates and containing mesogenic groupscompatible with the mesomorphic phase of component B.
 11. The precursoraccording to claim 10 wherein the comb polymers of the surface agent Chave a siloxane skeleton and the methacrylate function in the sidechain.
 12. The precursor according to claim 1, wherein component Acomprises monomers or oligomers, which by cross-linking in the presenceof other compounds will provide a plastic material, and wherein surfaceagent C is a surface active agent which controls the interfacialproperties of said liquid crystal and said polymer to induce a temporaryspatial non-uniformity of the material.
 13. The precursor according toclaim 12, wherein said plastic material is a gel or micro-composite. 14.The precursor according to claim 12, wherein said precursor has inweight proportion: 60 to 80% of component A 40 to 20% of component B andwherein said surface agent C represents 1 to 5% of the whole ofcomponents A and B, in weight proportions.
 15. The precursor accordingto claim 12, wherein said precursor has, in weight proportions: 70 to97% of component B 30 to 3% of surface active agent C and component A.16. The precursor according to claim 12 wherein component A comprisesmonomers selected from acrylates or methacrylates, component B is aliquid crystal or a mixture of liquid crystals, and wherein the surfaceagent C comprises comb polymers having reactive groups selected fromacrylates or methacrylates and containing mesogenic groups compatiblewith the mesomorphic phase of component B.
 17. The precursor accordingto claim 12 wherein the comb polymers of the surface agent C have asiloxane skeleton and the methacrylate function in the side chain.